Abnormal hyperphosphorylation and aggregation of tau protein in the brain are critical to neurodegeneration of Alzheimer diesease (AD). Glucose uptake/metabolism is impaired in AD brain, which is believed to cause neurodegeneration. However, how this impairment contributes to neurodegeneration is unknown. The specific goal of this project is to reveal the nature and functional role of tau O-GlcNAcylation [a unique type of O-glycosylation by which beta-N-acetylglucosamine (GlcNAc) is linked to serine or threonine residues of proteins] and to uncover the mechanism by which impaired brain glucose uptake/metabolism of AD contributes to neurodegeneration. The long-term objective of this proposal is to understand the mechanism of neurodegeneration in AD and, based on this knowledge, to develop strategies to prevent and treat the disease. Hence, the specific aims are: (1) Map the O-GlcNAcylation sites of tau and determine the change of tau O-GlcNAcylation in AD brain. The underlying cause of the change in tau O-GlcNAcylation will also be studied by comparing brain level of UDP-GlcNAc and activities of O-GlcNAc transferase and O-GlcNAcase between AD and controls. (2) Study the interactions between O-GlcNAcylation and phosphorylation of tau both in vitro and in differentiated PC12 cells. The functional role of tau O-GlcNAcylation will be studied by measuring its microtubule-binding and -assembly activities and examining cell morphology and organelle transport upon alteration of tau O-GlcNAcylation. (3) Investigate the molecular mechanism by which impaired brain glucose uptake/metabolism contributes to neurodegeneration of AD. Two animal models of impaired brain glucose uptake/metabolism[unreadable]fasted mice and mice after intracerebroventricular injection of cytochalasin B[unreadable]will be used to study its effects on tau O-GlcNAcylation and phosphorylation. The exact role of O-GlcNAcylation in tau hyperphosphorylation and neurodegeneration induced by low glucose uptake/metabolism will also be elucidated in the mouse brains. These studies will reveal the nature and functional role of tau O-GlcNAcylation and its dysregulation in AD brain and uncover the mechanism by which impaired brain glucose uptake/metabolism of AD contributes to neurodegeneration. Completion of these studies will provide new insight into the mechanism of neurodegeneration of AD and help develop novel strategies to prevent and treat AD and probably other neurodegenerative disorders.